A technique of a recent navigation system is known to provide a detour for avoiding traffic congestion when acquiring information of traffic congestion, etc. on a road on which the vehicle is traveling. In Patent Document 1 described below, for example, the technique is described in which, when a navigation system acquires information indicating that traffic congestion TG has occurred on a reference route (initial guidance route RU1), which is a route obtained by searching from a departure point to a destination, the navigation system presents a temporary route (detour DR) for avoiding the traffic congestion TG. Then, in a case where the vehicle travels along the temporary route and the same destination is set later, a route including the temporary route is employed as a normal travel route (basic route) and is preferentially presented for guidance.
In this manner, in Japanese Patent Application Publication No. 2004-340641 (JP 2004-340641), in a case where a vehicle travels along a temporary route because of occurrence of traffic congestion on a reference route, the temporary route is employed as a normal travel route thereafter.